1. Field of the Invention
The present invention relates to the field of blade assemblies for a turbomachine compressor, such as a turbojet or a turboshaft engine for a helicopter. The invention also relates to a compressor comprising such a blade assembly, in particular a rectifier for a high pressure compressor.
2. Description of the Related Art
It is known that the compression system for a turbojet (and the high pressure compressor, in particular) is one of the most critical components of the engine. The compressor of a turbojet consists of a plurality of successive compression stages, each stage comprising two blade assemblies, namely a rotor and a rectifier (stator). The rectifier comprises, in the usual manner, an internal shroud and an external shroud which are coaxial, in addition to blades which are arranged adjacent to one another between said internal and external shrouds and which are connected thereto by their ends, as disclosed, for example, in the document FR-2 896 019.
To ensure the operation of a compressor, clearance is present at each stage between the rectifier and the hub, forming a cavity below the rectifier. Generally, a leakage flow circulates in said cavity, in the direction from downstream to upstream of said rectifier, passing below the radially internal end of the internal shroud. Said leakage flow is then reinjected into the airflow, upstream of the rectifier.
Said leakage flow interferes with the principal flow and contributes to the generation of stall. In particular, it alters the flow conditions upstream of the blades, it promotes the occurrence of corner stall and increases the associated losses.
Thus, two main sources of losses coexist in this area of the compressor: those due to the recirculation below the stator and those caused by corner stall.
In addition, to reduce the losses effectively, it is necessary to take action on both of said phenomena at once.
To reduce stall, a system which uses vortex generators arranged on the hub, upstream of the fixed or mobile wheels of a compressor, is disclosed in the document WO-2008/046389. Said vortex generators which are provided on the upstream internal and/or external duct wall generate wake vortices which increase the energy of the boundary layer on the channel wall. An increase in the flow component is produced in the direction of the principal flow, in the vicinity of the wall, which advantageously acts on the stall in the region of the fixed and mobile blades.
The system disclosed in said document WO-2008/046389 which solely acts on the principal flow only deals with one of the two aforementioned problems of stall, even though said two problems are associated. This usual solution is thus not completely satisfactory to reduce losses in the region of the rectifier.